1. Field of the Invention
The present invention relates to a motion compensating apparatus which is applied to a digital image transmitter, a digital CATV or a digital broadcasting system.
2. Description of the Related Art
FIG. 18 is a block diagram explaining a conventional digital image coding system which is shown in an article entitled “DEVELOPMENT OF MPEG2 REAL TIME CODING SYSTEM CHIP SET”, Denshi Jouhou Tsuushin Gakkai Gijutsu Kenkyuu Houkoku, Vol. 95, No. 217, pp. 2 to 8 (1995).
In FIG. 18, reference numeral 400 denotes a motion compensation processing unit for receiving as inputs thereof an input image 202 and reference images 152 to output an estimated image 204 and an optimal vector 449; reference numeral 222 denotes a differential unit for obtaining a difference between the input image 202 and the estimated image 204 to output a residual signal 223; reference numeral 401 denotes a difference signal coding processing unit for coding the residual signal 223 inputted thereto to output difference coded data 450; and reference numeral 402 denotes a motion vector coding processing unit for coding the optimal vector 449 inputted thereto to output motion vector coded data 451.
Next, the operation of the conventional digital image coding system as configured above will hereinbelow be described.
The motion compensation processing unit 400 receives as the inputs thereof the input image 202 as the image of the current frame and the reference images 152 as the image of the former frames to retrieve the image which bears the closest resemblance to the input image 202 from the reference images 152.
The retrieval method is such that the sum of difference absolute values between the input image 202 and the reference images 152 and the image among the reference images which gives the most small distortion is made to be the optimal image, i.e., the estimated image 204. In this connection, as shown in FIG. 19, the motion vector exhibits how far the optimal image (the estimated image) moves spatially from the position of the input image in the current frame.
The motion vector is transmitted as the optimal vector 449 to the motion vector coding processing unit 402 which codes in turn the optimal vector 449 thus transmitted thereto to output the resultant information.
On the other hand, with respect to an estimated error signal which has been obtained after estimation by the motion compensation processing unit 400, the difference between the optimal estimated image 204 which has been selected by the motion compensation processing unit 400 and the input image 202 is obtained by the differential unit 222 and the residual signal 223 is coded by the difference signal coding processing unit 401 to be outputted.
The amount of generated information in the coding processing of this processing is the value which is obtained by summing the information amount of the difference coded data 450 which is generated in the difference signal coding processing unit 401 and the information amount of the motion vector coded data 451 which is generated in the motion vector coding processing unit 402.
In the conventional apparatus, as described above, the vector exhibiting the minimum value of the sum of difference absolute values is selected as the optimal vector in the motion compensation processing unit 400.
In the image coding processing, however, the vector which has been selected as the optimal vector in the motion compensation is coded (motion vector coding) and at the same time, the residual (the estimated error) between the current block and the former block of the optimal vector position is coded (residual coding).
Then, the information which is obtained by summing the information amount obtained by the motion vector coding and the information amount obtained by the residual coding becomes the amount of coded information.
For this reason, for example, in the case where the information amount becomes very large after completion of the coding of the optimal vector, or the like, the optimal vector which is selected by the above-mentioned method does not always minimize the amount of coded information.
In addition, while in general, the vector is obtained in the motion compensating estimation using only the luminance information, for the images in which the luminance signals are identical to each other but the color difference signals are different from each other, the wrong motion vector is extracted.